In some WiFi capable devices for use in WLANs (Wireless Local Area Networks), users may create profiles for networks and/or APs (Access Points) to which they commonly connect. These profiles are stored in profile tables or lists on the devices to enable the devices to automatically connect to a network listed in the profile table for that device when the device in the range of that network. A profile usually contains an SSID (Service Set Identifier) for the network and security parameters, such as whether the network is Open or Secure and security keys.
Each AP in a WLAN has one or more MAC (Medium Access Control) address for the AP and one or more SSID for the networks to which the AP belongs. Some networks have what is known as “hidden SSIDs”. A hidden SSID is not disclosed in response to a scan or probe for availability of the network, or in the beacon that the AP transmits regularly. To join such a network, a user must know the SSID and usually the user will conduct a directed probe using the known SSID to check availability.
Some WiFi capable devices perform scans and probes in accordance with IEEE Standard 802.11 to determine which APs and/or peer devices are available. A broadcast probe request is sent to determine all APs and/or devices that are WiFi capable in the range of the user device. Each AP/device found sends a probe reply containing its respective MAC address. The probe reply also indicates whether or not the address belongs to an infrastructure device, such as an AP, or an independent wireless device, such as a laptop or handheld device. The probe reply will also include the SSID, if it is not hidden. Broadcast probe requests are also known as broadcast scans or site surveys. After the probe reply is received, the results are stored on the wireless device, usually in (Random Access Memory). A user can then select an AP/device from the scan results and connect to that device it the SSID is not hidden. Furthermore, scanning can be defined as either passive or active. Passive scanning involves listening for the beacon transmitted by the AP. Active scanning is performed by sending “probe request” packets to a broadcast MAC address. If the probe request packet contains an SSID, then it is known as a directed probe. If the probe request does not contain an SSID it is known as a broadcast probe or discover probe.
Directed probe requests that are sent directly to a specific network are also possible. In order to send a directed probe request the user must know the SSID of the network of the AP or device.
Typically, a WiFi capable device will send a broadcast probe first to determine all APs or other mobile device to which it can connect. If some of the APs listed in the scan result have hidden SSIDs, some devices are programmed to go through each profile stored on the device and send a directed probe to each SSID to ensure that all of the available APs from networks listed on the profile table for that device are added to the scan result. If the list of profiles is long, this can be time consuming. Furthermore, each probe uses valuable battery power in battery operated mobile devices because rather than putting the mobile device in sleep (or doze) mode, the mobile device is in active mode transmitting and/or receiving packets such as beacons, probe requests, probe responses, etc.